The present invention relates to fiber optic transmission systems and, more particularly, to an arrangement for monitoring the qualities of spare fibers within a fiber optic cable.
Fiber optic cables as used in most communication networks have fiber counts that range from twenty-four to upwards of 216 individual fibers. Not all of these fibers are ever in service at the same time, as some will be designated as xe2x80x9csparexe2x80x9d fibers within the cable, and available as replacements if and when other fibers begin to fail. There are various methods well-known in the art that are used to continuously test and monitor the fibers that are actively being used for transmission. One well-known method uses a method referred to as optical time-domain reflectometry (OTDR) which is, in effect, a xe2x80x9claser radarxe2x80x9d system which tests the conditions of an active fiber by injecting laser beam pulses into the fiber at one point and then receiving returned reflections of the pulses. The time elapsed between the sending and the receiving, as well as the pulse shape, is used to diagnose the condition of the fiber and determine when the fiber has failed.
During normal operating conditions, however, the spare fibers are left xe2x80x9copenxe2x80x9d; that is, not connected to any equipment and, therefore, these spare fibers are never monitored. When a need arises to use one of the spare fibers, a technician must travel to the location where the spare fiber is to be spliced in place of a failed fiber and use the OTDR method (or any other appropriate method) to first verify the integrity of the spare fiber. At times, the spare fibers themselves are defective and will require maintenance prior to connecting them to the communication equipment.
Thus, a need remains for a method of providing a continuous monitor of the condition of spare fibers within a fiber optic cable.
The need remaining in the art is addressed by the present invention, which relates to fiber optic transmission systems and, more particularly, to an arrangement for monitoring the qualities of spare fibers within a fiber optic cable.
In accordance with the present invention, a spare fiber monitor system includes a transmitter portion at a first location including a plurality of laser sources for generating a plurality of test signals. The xe2x80x9csparexe2x80x9d fibers are then coupled into the transmitter and the test signals are launched along these fibers. A receiver portion is located a predetermined distance away (such as, for example, at the next regenerator location) for receiving the plurality of test signals propagated along the spare fibers. Threshold detectors (or any other suitable monitoring arrangement) are used to analyze the power level of the received test signals. The receiver includes an alarm indicator which will be activated when one (or more) of the spare fibers experiences a failure. Thus, a technician can either repair the failed fiber or (at a minimum) not use the failed spare fiber when the need arises to replace a failed transmission fiber with a spare fiber.
In one embodiment of the present invention, the alarm indicator at the receiver is used in a xe2x80x9clocal alarmxe2x80x9d mode to alert a technician at the remote location regarding the failure of the spare fiber. Alternatively, the alarm indicator may include a telemetry capability to send an alert signal back to the transmitter to be dealt with by a technician at the transmitter location.